Constitutive modeling and microstructure characterization of 2196 Al-Li alloy in various hot deformation conditions

Abstract

• A constitutive model with comprehensive consideration of temperature, strain rate and strain compensation was proposed. • Processing maps under different strains were generated. • The peak power dissipation domain is located in high temperature and medium strain rate. • Dynamic recovery is the main softening mechanism with a small amount of continuous dynamic recrystallization. • The optimum deformation parameters of 2196 Al-Li alloy were determined. Isothermal compression tests of 2196 Al-Cu-Li alloy were carried out at different temperatures (633∼793 K) and strain rates (0.001∼10 s −1 ) on Gleeble-3500 thermal simulator until the compression reached 60 %. According to the obtained stress-strain data, the flow behavior of 2196 Al-Li alloy during thermal deformation was investigated. The Arrhenius constitutive equation of the alloy based on the hyperbolic sine function model was established. A modified constitutive model with comprehensive consideration of deformation temperature, strain rate and strain compensation was proposed. Compared with the traditional constitutive model of strain compensation, the modified model had higher prediction accuracy. The hot processing maps under different strains (0.2∼0.8) were established, it was found that the plastic instability domain mainly occurred at the low temperature and high strain rate, while the peak power dissipation domain was located in the high temperature and medium strain rate. The microstructure evolution of 2196 Al-Li alloy under different deformation conditions was characterized and analyzed by electron back scattering diffraction and transmission electron microscope. The results showed that the softening mechanism was mainly dynamic recovery with a small amount of continuous dynamic recrystallization. High temperature and low strain rate were conducive to the occurrence of dynamic recovery and recrystallization, and the microstructure was mainly characterized by low dislocation density, no dislocation entanglement and dislocation wall structure. The grain boundary was straight and smooth. Some discontinuous dynamic recrystallization occurred at low temperature and high strain rate. Based on the analysis of the hot processing maps and microstructure evolution, the optimum deformation parameters of 2196 Al-Li alloy were determined to be 733∼793 K and 0.01∼1 s −1 .